This application is based on and incorporates herein by reference Japanese Patent Applications No. 2000-272222 filed on Sep. 7, 2000 and No. 2000-304725 filed on Oct. 4, 2000.
The present invention relates to an automotive generator control apparatus for controlling an output voltage of an automotive generator by turning on and off a field coil current.
Automotive generators recharge a battery during vehicle engine operation in addition to providing power for engine ignition, vehicle lights, and other electrical equipment. A generator controller is connected to the generator for maintaining a substantially uniform output voltage even when the electrical load changes. Demand for reduced noise from the generator has increased with rising demand for higher automotive quality.
One method proposed to reduce generator noise is described in Japanese Patent Application Laid-open No. 64-20000, which teaches a method for reducing the switching noise signal that occurs when a field coil current is controlled by a MOS transistor. Switching noise signal is reduced with this method by negative feedback of a supply voltage from a voltage booster circuit to the gate terminal of the transistor so that the source voltage of the transistor follows a particular voltage step-up curve. The problem with this method is that the circuit design is complex and operation is likely to become unstable.
With another method proposed in Japanese Patent Application Laid-open No. 4-96696, when a transistor controlling a field coil current is conductive, current supply to the gate of the transistor is restricted until the source voltage of the transistor rises to a particular level. Thus, transistor conducting speed is slowed down to reduce switching noise signal. However, intermittent operation of a charge pump circuit used as a voltage booster circuit produces gate voltage current supply fluctuations, resulting in changes in, transistor current continuity. Conduction current change alone is a cause of switching noise signal. It is desirable to further reduce switching noise signal by suppressing this current change.
It is therefore an object of this invention to provide a control apparatus for a motor vehicle generator capable of reducing switching noise signal in a simple circuit configuration.
An automotive generator control apparatus according to the present invention has a switching device for interrupting current supply to a field coil of an automotive generator. A flywheel diode is parallel-connected to the field coil. A voltage detection circuit is provided for outputting a signal instruction to turn on or off the switching device so that the output voltage of the automotive generator is adjusted to a specified voltage. A drive circuit is provided for driving the switching device.
When a signal instructing the switching device to turn on is input from the voltage detection circuit, the drive circuit supplies a specific current to a switching device control terminal to raise the control terminal voltage until terminal voltage of the field coil exceed a specified value. After terminal voltage of the field coil rise to the specified value, the drive circuit applies a voltage higher than the output voltage of the automotive generator to the control terminal.
Because the switching device is driven by supplying the specific current until terminal voltage of the field coil rises to the particular value, change in current flow through the switching device is suppressed and switching noise signal in the output of the vehicle generator can be reduced. It will be noted that noise is reduced using a relatively simple circuit design because only elements for supplying the specific current are added to the circuit configuration generating a voltage higher than the output voltage of the automotive generator.
Alternatively, the drive circuit has a charge pump circuit having an even number of capacitor stages. A current supply circuit is provided for supplying current to the charge pump circuit. A signal circuit is provided for intermittently operating the charge pump circuit. A diode is connected in the forward direction from the input to the output terminal of the charge pump circuit.
The last capacitor in the charge pump circuit is charged when the first capacitor discharges, but the output current of the current supply circuit at this time is supplied to the control terminal of the switching device through the diode connected in the forward direction from the input terminal to the output terminal of the charge pump circuit. By supplying the output current of the current supply circuit to the control terminal of the switching device when the output current of the charge pump circuit is not supplied, change in the switching device drive current can be suppressed, change in current flow through the switching device can also be suppressed, and switching noise signal in the automotive generator output can be reduced. Furthermore, this can be achieved using a relatively simple circuit design because only the diode is added in parallel with the charge pump circuit.